Showing papers by "Neil Gordon published in 2017"

Single-Ended Differential Protection in MTDC Networks Using Optical Sensors

Abstract: This paper presents a method for rapid detection of faults on voltage source converter multiterminal HVdc transmission networks using multipoint optical current sensing. The proposed method uses differential protection as a guiding principle, and is implemented using current measurements obtained from the optical current sensors distributed along the transmission line. Performance is assessed through detailed transient simulation using MATLAB/Simulink models, integrating inductive dc-line terminations, detailed dc circuit-breaker models, and a network of fiber-optic current sensors. Moreover, the feasibility and required performance of optical-based measurements is validated through laboratory testing. Simulation results demonstrate that the proposed protection algorithm can effectively, and within very short period of time, discriminate between faults on the protected line (internal faults), and those occurring on adjacent lines or busbars (external faults). Hardware tests prove that the scheme can be achieved with the existing, available sensing technology.

Compact eccentric long period grating with improved sensitivity in low refractive index region.

Abstract: We demonstrate a compact eccentric long period grating with enhanced sensitivity in low refractive index region. With a period designed at 15 µm for coupling light to high order cladding modes, the grating is more sensitive to surrounding refractive index in low refractive index region. The intrinsically low coupling coefficients for those high order cladding modes are significantly improved with the eccentric localized inscription induced by the femtosecond laser. The fabricated grating is compact with a length of 4.05 mm, and exhibits an average sensitivity of ~505 nm/RIU in low refractive index region (1.3328-1.3544). The proposed principle can also work in other refractive index region with a proper choice of the resonant cladding modes.

Stealth dicing of sapphire wafers with near infra-red femtosecond pulses

Abstract: The quality of the reflecting faces after dicing is critical for the fabrication of efficient and stable laser diodes emitting in the green–violet region. However, high-quality faces can be difficult to achieve for devices grown on a sapphire substrate as this material is difficult to cleave cleanly. We have therefore investigated a technology known as “stealth dicing”. The technology uses a pulsed laser to damage a plane of material inside of the wafer due to multi-photon absorption instead of cutting through the wafer surface. If the damage is induced in a line of stress points, the sample can then be cleaved easily along the damaged plane to leave a high-quality surface. The use of this technique also reduces thermal damage and debris.

Femtosecond laser inscribed axial long-period fiber gratings in two-mode fiber for efficient optical angular momentum generation

Abstract: We demonstrate a novel all-fiber mode converter based on an axial long-period fiber grating which was inscribed in two-mode fiber using a femtosecond laser. The OAM ±1,1 modes can be effectively generated using this mode converter.

Distributed sensing for marine electrical system monitoring and protection applications

Abstract: In this paper, technology developed at the University of Strathclyde which has resulted in the commercialisation of distributed point sensors for electrical and mechanical parameters will be described. While primarily targeted at terrestrial power system applications to date, this technology has significant potential for realising novel and effective monitoring and protection solutions for marine electrical systems. In the paper, the technology and its capabilities will be reviewed, and a number of potential applications will be described and discussed briefly. Many of these applications can assist in reducing the levels of risk associated with marine electrical systems, through delivering comprehensive monitoring and protection functions that benefit from the distributed nature of the measurement system. The measurement system will be outlined and it will be shown how it consists of a central interrogator that uses optical fibre to collect several measurements from a distributed, and, importantly, completely passive, array of sensors that are connected along the length of the fibre, which can be up to 100 km in length (clearly adequate for any marine applications). Finally, the paper will describe a number of distributed monitoring and protection applications in marine electrical systems that can be facilitated by the distributed measurement system.

How Statistical Signal Processing Was Used to Define the MH370 Search Zone

Abstract: Malaysian Airlines flight MH370 from Kuala Lumpur, Malaysia, to Beijing, China, departed on 8 March 2014 carrying 239 passengers and crew. Communications with the aircraft were lost as it transitioned from Malaysian to Vietnamese airspace, and the subsequent search and rescue efforts were unable to find the missing aircraft. Radar data indicates that the aircraft turned to the southwest and crossed Malaysia and then f lew northwest along the Malacca Strait. When the aircraft moved beyond radar coverage, it was still carrying enough fuel to fly for several hours, and the size of the reachable area is almost 20% of the surface of the Earth. Although communications were lost early in flight, there was an active communications link between the aircraft and a satellite; metadata from signaling messages on the link provide information about where the aircraft was, even though no user data was communicated.